A small animal model for hepatitis B viral (HBV) infection is unknown to date. The woodchuck infected with Woodchuck Hepatitis Virus (WHV) is the best infection model available, yet it has inherent limits including its size and breeding patterns. Producing sufficient drug for testing in the woodchuck was problematic for many companies. To facilitate more rapid and HBV-specific testing, an HBV-producing transgenic mouse model was developed by grantees, Drs. Chisari and Guidotti. This model was subsequently transferred to Utah State University through the NIAID. Limited in that this model carries a transgene and therefore cannot be used for pathogenesis studies, proof of principal studies have shown it can detect efficacy of antiviral and immunomodulating drugs. Promising candidate antivirals tested initially in well-defined in vitro screens can subsequently move into in vivo testing through the HBV Animal Model Network-a consortium of three contracts involved in this endeavor.